With the advance in genetic engineering, recently, development and studies on medicaments have been actively carried out, which use bio-related substances such as intercellular signaling substances such as hormones and cytokines, antibodies, and enzymes. Since these bio-related substances are usually cleared from a living body because of the filtration through glomeruli in the kidney and the uptake by macrophages in the liver, spleen, and the like when the substances are injected to the body, they have short half-lives in blood and hence it is difficult to obtain a sufficient pharmacological effect. For solving the problems, it is attempted to improve the behavior in a living body by including the bio-related substances in liposomes or polymer micelles or increasing their molecular weight or forming a hydration layer through chemical modification with an amphiphatic polymer such as a sugar chain or polyethylene glycol or albumin. In the modification with a polyoxyalkylene compound, effects of decreasing toxicity and antigenicity and enhancing solubility of sparingly water-soluble pharmaceuticals are also obtained but, excessive modification of the polyoxyalkylene compound breaks the active points of the bio-related substances and reduces functions thereof, so that it is attempted to enhance the effects by increasing the molecular weight of the polyoxyalkylene compound. However, since an increase in the molecular weight results in an increase in viscosity in the polyoxyalkylene compound, there arises a problem that it is difficult to handle it, for example, in solution preparations such as an injection preparation, so that there has been advanced the development of polyoxyalkylene compounds having a branched structure in which viscosity is improved.
Patent Document 1 describes a polyoxyalkylene compound which branches into two chains. This is a compound in which two polyoxyalkylene chains form, together with glycerin, an ether bond which is hardly decomposed into one chain.
Furthermore, as a polyoxyalkylene compound having a multibranched structure, Patent Documents 2 and 3 describe a polyoxyalkylene compound having a tetrabranched structure containing triglycerin as a fundamental skeleton. However, since it uses triglyceryl monoallyl ether as a starting material, in the case where the allyl ether part is subjected to functional group conversion, the conversion is limited to compounds having a sulfur atom. Moreover, in the case where polymerization reaction with an alkylene oxide is carried out under an alkali catalyst, there is a concern that the allyl ether is rearranged into a propenyl ether and then converted into a hydroxyl group during a neutralization step, resulting in a decrease in purity.
Patent Document 4 describes a polyoxyalkylene compound having a tetrabranched structure containing 1,2-glycerol as a fundamental skeleton. This is a polyoxyalkylene compound having a dibranched plus tetrabranched structure in which polyoxyalkylene terminal ends having a dibranched structure further branch into dibranched chains. However, since the compound has the dibranched structure in the molecule, in the case where it is transformed into an aqueous solution, it is considered that the compound shows a high viscosity as compared with a polyoxyalkylene compound having only a tetrabranched chain. Moreover, also in synthesis, since the structure is complex, there is a problem that a variety of impurities form.
As described above, a polyoxyalkylene compound having a multibranched group chain structure of four or more chains capable of being effectively used in applications for modifying bio-related substances and industrially easily produced is not obtained, so that it has been desired an appearance of such a multibranched polyoxyalkylene compound.